1. Field of the Invention
This invention relates to voltage regulators, and more particularly to switching/chopper regulators and to active filters.
2. Description of the Prior Art
In the prior art, voltage regulators have been described utilizing a chopper in combination with a transformer and rectifying circuitry to boost the voltage of a direct current voltage bus. One example of a voltage regulator which boosts the voltage of an unregulated input DC bus is shown in U.S. Pat. No. 2,965,833 issued on Dec. 20, 1960 to J. L. Jensen entitled "Semiconductor Voltage Regulator Apparatus". Jensen shows a chopper which is used to convert a DC voltage to an AC voltage which is coupled into the output by means of a transformer and a rectifying bridge to convert the AC voltage to a direct current voltage which boosts the input voltage resulting in a regulated output voltage.
Another system that uses an injection technique for regulating the voltage is described in U.S. Pat. No. 3,896,368 issued on July 22, 1975 to Christian Rym. In the patent to Rym, the DC voltage to be regulated is compared with a reference voltage to generate an error signal. The error signal is fed to an analog to digital converter which converts the error signal to a digital value where each bit of the digital word is used to control switching in or out solar cell panels having a predetermined supply current. The supply current in each module is sized to correspond to the bit it is associated with in the digital word. Course voltage adjustment is therefore provided by switching in modules providing a fixed DC current dependent upon the value of the digital word. As the error signal values vary, the value of a digital word will likewise vary and the current switched onto the voltage bus will likewise vary to minimize the difference between the voltage on the supply bus and the reference voltage. Fine adjustment of the voltage bus is accomplished by using smaller bits of the digital word from the analog to digital converter to switch in loads having corresponding binary weighting onto the voltage bus. The loads act as current sinks to draw current off the voltage bus and therefore reduce the voltage on the voltage bus to achieve fine adjustment. In summary, a number of current sources each having a binary weighting and a number of loads each having a binary weighting are made available to be switched in or out of the voltage bus depending upon the error signal and the digital word generated from the error signal.
Another voltage regulator exemplary of the prior art is shown in U.S. Pat. No. 3,419,788 issued on Dec. 31, 1968 to J. C. May. In May, a series of boost injecting transformers are aligned in series between the unregulated voltage and the power line to be regulated. Individual square wave inverters are used for each transformer. This particular regulator is oriented for regulating alternating current where each transformer injects voltage, the amplitude of the voltage is controlled by an adjustable DC power supply and the time of injection is adjusted to correspond with the phase of the alternating current. Each boost injector or transformer is turned on for a predetermined time with relation to the phase of the AC voltage of the line to be regulated such that the summation of all the boost injectors results in an approximated sine wave which is added to the AC voltage to result in an increase in amplitude of the AC voltage. The current from the unregulated terminal must pass through a winding of each boost transformer before reaching the regulated power bus. The control of each individual square wave inverter and transformer is provided by an oscillator and logic circuit. An alternate embodiment varies the phase of the approximated sine wave with respect to the AC voltage to be regulated. Each individual boost transformer provides positive polarity for half of the alternating current cycle and negative polarity for the other half. The boost transformers, therefore, operate at the same frequency as the AC voltage it is regulating.
Other methods to provide regulation of DC power supply lines include passive components such as capacitors and inductors to act as filters and to provide reserve energy to maintain the voltage on the DC buses in situations such as extreme power brownouts. Another prior art means of regulating voltage consists of a linear regulator placed in series with the line to be regulated and provides a constant output voltage by varying the voltage drop across the linear regulator. A linear regulator may consist of, for example a transistor having its collector connected to the unregulated voltage bus and its emitter connected to the regulated bus. A sense circuit provides an error signal which is coupled to the base of the transistor which determines the amount of current that passes through the transistor and the voltage drop across the transistor. Linear regulators absorb considerable power since they provide a voltage drop in series with the total current that is used by the power bus.
It is therefore desirable to provide a voltage regulator which will provide active filtering at high efficiency, and remove the need to use large storage elements to prevent the effects of line dropouts.
It is further desirable that the regulator pump frequency have an ample frequency range so that the pump frequency may be locked to a multiple of the PRF of a radar system to control the frequency spectrum of any radiation.
It is further desirable to maintain the output voltage constant under extreme power brownouts utilizing a high frequency voltage regulator.